Icon handling problems 

There is a problem in Xfce GUI (Xfce 4.12.3 Distro: Linux Mint 19 Tara) 
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The problem: 

When I sending icon from Xfce Menu to the Panel, not the desired icon appears on the Panel. 
For example: I send the Firefox icon from Menu, and appears the Terminal icon on the Panel.
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This problem wasn't on 18.X Mint with Xfce.   


my System Parameters: 
System:    Host: pc1 Kernel: 4.15.0-24-generic x86_64 bits: 64
           Desktop: Xfce 4.12.3 Distro: Linux Mint 19 Tara
Machine:   Device: desktop Mobo: ASUSTeK model: PRIME B250M-C v: Rev X.0x serial: N/A
           UEFI [Legacy]: American Megatrends v: 1205 date: 05/11/2018
CPU:       Dual core Intel Core i3-6100 (-MT-MCP-) cache: 3072 KB
           clock speeds: max: 3700 MHz 1: 3685 MHz 2: 3421 MHz 3: 3629 MHz
           4: 3642 MHz
Graphics:  Card: NVIDIA GF119 [GeForce GT 610]
           Display Server: x11 (X.Org 1.19.6 )
           drivers: nvidia (unloaded: modesetting,fbdev,vesa,nouveau)
           Resolution: 1920x1080@60.00hz
           OpenGL: renderer: GeForce GT 610/PCIe/SSE2
           version: 4.6.0 NVIDIA 390.48